Hi Rosie,
You will find smooth top mattresses in most price ranges depending on the quality of the materials inside the mattress but a lot of budget innerspring mattresses will have one because most of the padding is in the quilted cover instead of inside the mattress itself.
The mattress quilting helps the mattress to keep its shape and prevent the foam from shifting and the quilting (or tufting) can also precompress the foam in a cover which can help with durability. It’s also used because many mattresses include the fire barrier as part of the cover so the quilting is what is used to “attach” it to the the cover. You will find many quilted mattresses that are closer to a smooth top which don’t have the same type of “bumps” as a tufted cover but your testing will tell you if a mattress is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences).
I personally wouldn’t consider any mattress from Sleep Country and I would make sure you’ve read the tutorial post here which has all the basic information, steps, and guidelines you will need to make the best possible choices … and learn how to avoid the worse ones.
Phoenix